What's the most popular religion?

Dear Straight Dope:

Please settle a bet. What is the most popular religion in the world, as in
which one has the most followers?

— Kathryn Seay

The problem here is, how does one gauge popularity? Is Leonardo DiCaprio more popular that John Wayne? Madonna more than Bessie Smith? Much depends on where you live, your cultural upbringing, and your personal preferences. What may be popular for one group of people may not be so popular for another.

So what do we look at? I was going to look at the amount of people who had actually converted to a certain religion, but Dex reminded me that a lot of religions do not seek converts as agressively as, say, the Mormons or the Jehovah's Witnesses. And most do not proselytize at all. I mean, when was the last time you can recall having a Shinto missionary come knocking at your front door?

It seems that best we can do is look at the bare statistics for the number of worldwide adherents for the major religions, but we get into trouble doing that as well. Most religions, excluding Christianity, do not keep records of the number of followers. And even within Christianity there are differing ways of keeping count. Catholics will include everyone who has ever been baptized in a Catholic church, while most Protestant denomination count
by actual church attendance.

To make matters worse, oriental religions tend to blur at the edges of what they believe, so it is very possible that a person can be counted in more than one category. One can be grouped as both a Buddhist and a Shintoist in Japan, while in China, one can be a Confucian, a Taoist and a Buddhist all at once. (Or in the case of this author, a Zen Baptist.)

Given these caveats, here's what the worldwide scorecard looks like. From the 1998 Information Please Almanac we see that the #1 religion is (surprise, surprise) Christianity at about 1,955,229,000 members. This breaks down like so:

Roman Catholics : 981,465,000

Protestants : 404,020,000

Orthodox : 218,350,000

Anglicans : 69,136,000

Other Christians : 282,258,000

Strangely enough, if you count it as religion, atheism is #2 at 1,782,809,000. Muslims come in a decent third at 1,126,325,000 (83% Sunnis, 16% Shi'ites, 1% other).

Staff Reports are written by the Straight Dope Science Advisory Board, Cecil's online auxiliary. Though the SDSAB does its best, these columns are edited by Ed Zotti, not Cecil, so accuracywise you'd better keep your fingers crossed.